Voltage sensing circuits are well known in the art. Typically, they are circuits used in an integrated circuit device. In one mode of operation termed "power up" mode, they receive the input voltage signal and generate an output voltage signal when the input voltage signal has exceeded a minimal threshold. Prior to that, when the input voltage signal is below the threshold level, the voltage sensing circuit does not generate the output voltage signal. The output voltage signal can be used to disable certain critical portion of the circuit to prevent it from causing uncertain status due to either voltage level or system noise. In many applications where the integrated circuit module comprises a memory array, this is crucial to protect the integrity of the data that is stored in the memory array.
A voltage sensing circuit also operates in a "power down" mode. In a power down mode, when the input voltage signal falls below a minimal threshold level, then the voltage sensing circuit would decrease its output voltage signal to zero, thereby assuring that when the power supply voltage goes below the minimal threshold level, certain critical portion of the circuit is disabled, preventing it from causing uncertainty in the state of the memory stored in the memory array due to low voltage level or system noise.
Although voltage sensing circuits are well known in the art, they have typically consumed too much power in their operation. As the level of integration increases and as integrated circuits find increasing usage in low power consumption applications, such as battery powered notebook computers, it is desirable to have the voltage sensing circuit consume less power.